12. We ... for three hours before we decloed to take a break a)must be trekking b)had been trekking c) have been trekking

12. We had been trekking (b) for three hours before we decided to take a break. 14. A good way to beat (b) a problem is to think about it calmly and carefully. 22. There was thick black smoke (b) coming out of the burning building. 24. Mark said that he had had (a) a great team in London the previous summer. 28. What time does the train reach (c) Bristol? 29. Neither Annabel nor (c) Sue has ever flown in a plane.